Method of and apparatus for grinding glass



r w. TAYLOR. METHOD OF AND APPARATUS FORGRINDING GLASS.

APPLICATION FILED 061;"28. 1920.

Patented Dec. 27, 1921.

2 SHEETS-SHEET]- F/yih A HOME) w TAYLOR. METHOD OF AND APPARATUS FOR GRINDING GLASS.

APPLICATION FILED OCT. 28. 920- A Patented Dec. 27, 1921'.

2 SHEET$-SHEET 2- A 4 TTORNEY WILLIAM TAYLOR, OF LEICESTER, ENGLAND.

METHOD OF AND APPARATUS FOR GRINDING GLASS.

Specification of Letters Patent.

rammed Dec. 27, rear.

Original application filed October aa'me, Serial in. 128,235. Divide d and this application filed October28,1920. erla1lio.420,077.

To all whom it may concern Be itknown that I WILLIAM TAYLQR, a citizen of Great Britain residing at Leicester,'in the county of icestershire, England, have invented certain new and useful Improvements in Methods of and Ap aratus for Grinding Glass, fully describe and represented in the following specification and the accompanying drawings, forming a part of the same.

This invention relates to methods of and apparatus for grinding glass and similar hard, non-plastic. materials by means of abrasive wheels.

Heretofore, although abrasive wheels, and particularly wheels made up of particles of abrasive materials such as carborundum and the like bonded with fusible earth or in other ways, have been used very largely in grind ing metals, comparatively very l1ttle use has been made of such wheels in grinding glass. Before the advent of artificial abrasive wheels, certain natural stones were used for grinding the channels in What is known as cut glassware, and also for grinding the edges of spectacle lenses, and since their introduction artificial abrasive wheels have been used with some success for the above purposes as a substitute for the natural stones, but in such use they have not been run at thehigh velocities at which they are generally most efficient, nor have they been used with economy and success when much material has to'be removed. Nor have they been used for grinding the surfaces of .lenses.

The object of the present invention is to provide an improved method and means whereby glass and similar hard, non-plastic materials may be ground with .artificial abrasive wheels which shall make it possible to grindplane and curved surfaces accurately with a degree of efliciency and rapidity beyond what has heretofore been obtained in the grinding ofglass. Although the invention has been made with the idea'of utilizing artificial abrasive wheels, and finds rapidly moving abrasive wheel, particles'of abrasive protruding from the face of the wheel surface attack the metal, heating it somewhatby impact and friction, increasing its plasticity by such heating, and cutting away a portion of the metal in a more or less well defined way. Plastic action seems to be a necessary part of all real cutting rapidly moving abrasive surfaces. On the other hand, glass at ordinary temperatures has no plasticity; and when the pressure between the glass and the wheel is such as in the case of grinding metal would generate sensible heat and add to the efiiciency of the operation by increasing the plasticity of the metal which is being removed, the result in the case of glass is apparently to heat and expand the surface locally (it being a bad conductor of heat), and produce in the glass-strains which tend to detach splinters or particles from the surface. Such strains, together with the shock, pressure and tearing action of the surface of the abrasive wheel, shatters and breaks away the surface of the glass. When the abrasive wheel is applied in the usual way for grinding glass, that is, according. to the practice in surface grinding of metal, with the peripheral face of the wheel bearing against the glass with a relative movement between the glass and the wheel inthe direction of the plane of 'the wheel, and with the presaction, and has an important function in the so-called grinding of metal surfaces by sure of the wheel on the glass chiefly normal to the surface to be formed on the glass, the pressure of the wheel tends to oppose such separation'of the splinters or particles of. glass, and even when in spite of this, splintering and separation does occur, the splinters are unable to'escape freely, being trapped between the wheel and the glass and the surface being formed is damaged by such splintering. The tendency of the glass .to splinter under the action of the grinding wheel, thus interferes seriously with the grinding operation when this'is carried on accordingto the usual practice, which prac- -]l turn to advantage this splintering of the glass under the action of the grindin wheel,

with the result that the grinding weel not.

only may be, but desirably is, operated at a high rate of s eed, such as that which is em loyed in t e grinding of metal, and which I believe may be as high as conditions of safetypermit.

Instead of ap lying the grinding wheel to the glass in t e usual way, ll apply the grinding wheel to the work in such a way that an abrupt step or terrace is formed'between the unground or original surface and the ground surface of the work, which is best normal to, but which may be from say 80 to 110 to the original surface, and that I this step is cut backward bythe edge of the grinding wheel acting on the side of the step, a feeding movement belng caused'between the wheel and the work in a ohrec tion transverse to such step and transverse to the direction in which the successively active portions of the edge of the grinder move in the rotation of the grinder; and ii shape that face of the wheel which is contiguous to, or faces, the surface of the glass to be formed so that it makes contact-therewith only at the base of the step, the wheel acting only on the side of the step,-and the pressure of the wheel being in a direction approximately parallel to the surface to be formed and chlefly normal to theface of the step. In such terrace grinding it is,

the edge of the step which is continuously splintered by the action of the grinding wheel, and the detached glass articles are thus free to escape immediate y, their detachment and escape belng assisted, instead of being hindered, by the pressure of the wheel.

In grinding glassin this manner it is possible, and for the highest efiiciency desirable, to run the grinding wheels at high peripheral velocities such as are commonly employed in grinding metal with abrasive wheels.

much slower than has been customary heretofore in grinding glass with abrasive wheels, but this is much more than ofiset by the increased depth of cut or rate of feed.

The general application of terrace grindin is broadl claimed in' my copending ap phcatlon, Serial No.1i28,235, filed October On the other hand, the rate oi, traverse between the wheel and the work is 28, 1916,01? which the present application. is

a division. The present ap lioation is di-' rected particularly to a met odtor' grind ing spherical or approximately spherical surfaces incorporating my terracing method racin of sp faces. 7 v

Theaccompanying drawings illustrate .70 and to apparatus adapted to apply my ter-' method of grinding to the forming erical or approximately spherical sur more orless diagrammatically ap aratus? embodying the present invention an adapt ed to carry out a method embodying theinvention.

In said drawings- Figure 1 is a plan view,-:: artly in section, illustrating .diagrammaticall for grinding flat or convex? curved surfaces;

Fig. 2 is a viewsimilarto Fig. 1, but showing the grinding wheel adjusted for grinding a convex surface, and ig. Eris a or concavely an apparatussimilar view showing the grinding wheel adjusted for grinding a concave surface;

Fig. dis a side view of the apparatus. shown in lFi 1. I 'llhe' drawlngs illustrate an my method to the grinding and generating spherical surfaces'onlenses, the appam. U

tus shown being also adapted for the grindapplication of ing ofa plane surface on alens or other piece of glass orsimilar material. As illustrated grinding portion annular in cross-section,

to grind the surface oi the lens.

in the drawings the grinding wheel20 is a: cup-shaped" wheel. having a cylindrical 1 the annular edge of the wheel being applied The lens or disk of glass 21 to be ground is mounted in a chuck 22 on a rotating spindle 23 which is usually mounted so that it may be given lot a longitudinal feeding movement to feed the lens toward the edge of the grinding wheel.

The grinding'wheel is mounted with its axis of rotation in, or approximately in, a plane in which the axis of the work spindle 23 lies, and the wheel is set so that as it rotates its annular center'o the glass disk 21 carried by the work spindle; and the grinding wheel spini 11 dle 24: is mounted in bearings in a swinging support 25 mounted to turn about an axis which 1s perpendicular. to the axis of the igrinding edge will sweep over the work spindle and whichfin order to permit 7 the inchnation of the axes of the wheel spindle and work spindle-to be varied withoutdlsplacing the edge of the wheel from the center of-the work, passes through the line! 1: of the axis of the workspindle at the point of contact of the edge of the grinding wheel I with the work. The axes of the grinding.

wheel spindle and of'the work splndle may thus bevariously inclined to each other while remaining in the same plane, or in closely adjacent parallel planes, by swlnging the work spindle support about its swivel, such vary;

I surface may be ground on the glass disk and ing of the inclination of the axes causing no displacement of the edge of the grinding wheel from the center of the work. For taking up wear on the annular edge of the grinding wheel, provision is made for advancing the wheel longitudinally of its axis of rotation. as by forming its swinging support 25 of an upper part 2 adjustable in the direction of the axis of rotation of the wheel on a lower part 5. as shown in Fig. 4. The grinding wheel is driven at a high rate of speed, and the work spindle rotates at a low rate. The

upper part 2 of the support should also be transversely adjustable on an intermediate part 3 as shown, and the support is also formed to provide for vertical adjustment of the wheel as indicated at 4, such vertical adjustment permitting a small adjustment of the wheel in the direction longitudinal of the axis of its swinging support, so that the wheel may be set with its axis slightly above or below the plane of the work spindle axis which is normal to the axis of its swinging support.

iVhen the axis of the grinding wheel is set parallel to the axis of the work spindle, as shown in Fig. 4, a plane surface will obviously be ground on the glass 21 coinciding with the plane of the annular edge of the grinding wheel. If now the axis of(, the grinding wheel spindle be set at an angle to the work spindle as shown in Fig. 2, there will be ground on the face of the glass disk a portion of a sphere whose radius depends on the diameter of the annular edge of the wheel and on the angular relation between the axis of the work spindle and the axis of the grinding wheel spindle. If the spindles are set with their axes nearly at right angles as in Fig. 2, there will be ground on the face of the glass disk a. convex surface whose'ra+ dius approaches the radius of the grinding wheel. and at any intermediate angle at which the spindle axes may be set a curved surface will be ground whose radius is somewhere between infinity and this inner radius of the grinding wheel. By swinging the grinding wheel in the opposite direction so that the grinding is done by the outer edge of the wheel. as shown in Fig. 3 a concave the radius of curvature of such surface will similarly depend upon the angular relation between the axes of the two. spindles. By feeding the cup-shaped grinding wheel forward longitudinally of its axis of rotation as it wears away, and just enough to compensate for such wear, any change in curvature of-the lens produced is prevented. By providing graduations (not shown) on the swivel of the grinding wheel support, I facilitate the setting of the machine so that it may be readily set to grind curves of any desired radius.

'lel to the axis of the Wheel, according to whether a concave or a convex surface is being ground, and accordlng to the direction of rotation of the Work, so that the depth of out will be slightly greater on one side of the lens center than on the other; Terrace grinding will then take placeon the side of the greater depth of cut, and grinding more in the nature of ordinary abrasive action will take place on the other side of the center of the lens. I

The grinding wheel should be set so that its active edge ust slightly overlaps the axis of the work spindle, and the wheel should rotate in the direction so that its active edge shall move from the periphery toward the centerof the lens on the side of the deeper out where the terrace grinding is taking place, thereby reducing the risk of splintering the peripheral edge of the lens.

With the work spindle and the grinding wheel rotating in the directions indicated by the arrows in the drawings, the grinding wheel when set for grinding a convex lens, as shown in the plan view Fig. 2 should be set with its axis slightly below the work axis, and the annular edge of the grinder should be beveled both outwardly and in from the periphery of the lens inward on j that side of the center where the depth of cut is slightly greater, and on the other or lower side of the lens center where the depth of cut is less, abrasive action which is not true tel-racing will be accomplished by the inner portion of the end of the abrasive annulus which is beveled to give it clearance in the terracing action which takes place above the lens center. The difference in level of the two axes, that'is, the distance between the parallel planes of the two axes must be only very slight so that the abrasive action when the cut-has any appreciable depth shall take place clear across the lens surface. It is best to make the greatest depth of cut in grinding'curved surfaces in this manner less thanthe depth which is found most suitable and efficient for terrace grinding in other Ways, as, forexample, in grinding edges of lenses or in grinding planev surfaces. A

depth of cut of about .005" is cut on the v 5 wheels of suitable diameter any excessive deeper side of the center of the lens where the terracing action takes place from the periphery of. the glass to its center is ordinarily found about right: with a depth of say .002"

on the other side of the center where ordinary abrasive action may occur.

q In such case the rate of work rotation suitable for the terracing actionmay also suit the abrasive action, so that there is a substantial net gain in rate of grinding from emplo ing terracing action in the major part 0 the work.

When the grinding wheel is set for grinding a concave lens, as shown in plan in Fig.

other direction from the parallel plane of the 3, 1ts axis should be displaced slightly in the ax is'of the work spindle, orslightly above I the plane of the work spindle axis in the v p positionof the parts shown, so that in this '1 fore from the periphery of the lens inward 1 on the upp'erside of the center and ordinary case-terrace. grinding will take place as beabrasive actionwill take place below the lens.

1 I center. For such concave grinding, the edge ofthe grinding annulus may be formed about 1 as shown in Fig. 3 so that on .the port1on of the surface roundby the outer face of the grinding w eel an abrupt step will be formed and the inwardly extending edge or face of the annulus will clear the ground surface of the lens on this side of the center,

contacting therewith only at the base of the step. With regard to the angle of the step-' forming face or side of the grinding wheel,

it should benoted that such angle, and the- ;corresponding en lo of the step to the ground surface,-w1ll be less, that is, steeper,

toward the periphery of the lens than the angle shown at the center in. Fig. 3; and as the rotary movement of the lensgives the highest velocity at andnear the periphery where the step angle is best and material has to be removed from a greater perimeter,

the somewhat excessive angle at the center is not ordinarily objectionable. -By using 1 Jan le may be readily guarded against.

i t will .be understood that the vertical iadjustment of the 'swiveled or swingingsuport for the grinding wheel by the means indicated at4in Fig. 4: provides for setting the wheel axis slightly above or below the work spindle axis as and for the purpose ax s of the above described.

causmg a relaoreen sive wheel and the work in a direction parallel with the plane of the annular edge of the wheel, and the whole action would then be terracing action.

in carrying out the method described, a surface speed of the grinding wheel of about 5000 feet per minutehas usually been found most satisfactory, this being-a safe working limit for the artificial abrasive wheels suc as are" usually most desirable, and being about the speed which is considered the best practice in the case of grinding metals with abrasive wheels. On the other hand, the surface speed of the work, or the relative speed of movement between the work to the grindin wheel in the direction transversely of the e go of the latter, is far lower than is usual in metal grinding and less than is usual in rinding glass by theordinary methods.

n grinding spherical surfaces by means of a cylindrical cup wheel, in accordance with my terracing method, where the wheel sweeps continuously over the center of the glass and at this point the terracing vanishcs, it is impossible to have a deep cut, and it is necessary to compromise by running the work faster in order to obtain an eflicient rate of grinding. In such a-case a lens of. 2 inches diameter may be rotated at about reyolutions per minute, and the feeding movement between the work and the grinding wheel may be at about .002 to .005 inch per revolution of the work. As will be athcred from the above, the thickness of the steps or. terraces ground away, that is the rate of feed, may vary quite largely.

. Artificial abrasive wheels of a suitable degree of softness have been found most desirable for most grinding in accordance with mylterracing method, but the method is of course not to be limited to the use of such wheels, and other suitable grinding wheels may be employed. For example, in grinding curved surfaces of very small radius with a cup-shaped inding wheel, it has been found desirab e to use a diamond charged tubular metal cutter, or grinder, since an ordinary abrasive wheel of suitable small diameter would not have suiiicient durability. In using artificial abrasive wheels, it is most desirable that the bond holding the abrasive particles should be such as to holdthe same with such a degree of tenacity that the wheel shall be what is ordinarily called soft, so that when the particles of abrasive become somewhat blunt in use they may break out and expose fresh cuttin particles. This is the common action 0 such abrasive wheels, but in grinding glass in accordance with the present method 1t is de-' sirable to use wheels considerably softer than those which are best for grinding metal, and it is found desirable also to select wheels of degrees of softness to suit difierent kinds grinding wheel bein of glass, and generally the faster the work is crowded on the wheel the harder the wheel should be.

It is desirable that the grinding wheel and work be kept cool by' means of water or other suitable cooling agent, as usual in grinding operations. For this purpose, I direct by suitable means such as the nozzle shown at i in Fig. 1 a-jet of 'cooling liquid on to the activeside or face of the wheel at a point near the wheel axis where its velocity is low, the jet being directed in the direction of rotation of the wheel. The liquid is thus supplied to the wheel without splashing and s reads by centrifu al action outwardly to t e active edge of the wheel. Any suitable cooling liquid-or lubricant may be used for this purpose.

What is claimed is 1. The method of grinding curved surfaces of glass and the like hard non-plastic materials, which comprises rotating the glass to be ground upon an axis passing through the surface to be ground, applying the annular edge of a rapidly rotating grinding wheel to the surface to be ground, the grin ing wheel being set with its axis of rotation to one side of a plane parallel thereto and oontaim'n the axis of rotation of the glass, the axis 0 rotation of the grindin wheel being at an acute angle with the axis of rotation of the glass, and the grinding edge of the wheel passing approximately through the axis of rotation of the glass as it sweeps over the surface thereof, the annular edge of the shaped to forman abrupt step between t e ground surface and theoriginal surface of the glass on one side of the axis of rotation of the latter and to contact with the ground surface adjacent the step onl v of rotation of the glass being such that a substantial portion. of the material removed is removed by splintering the side of the step.

2. The method of grinding curved surfaces of lass and the like hard non-plastic materia s, which comprises rotating the glass to be ground about an axis passing through the surface to be ground, applying the annular edge of a rapidly rotating grindin wheel to. the surface to be ground, the grin mg wheel at the base of the step, the ratebeing set with its axis of rotation to one side of a plane parallel thereto. and containin the axis of rotation of the glass, the axis 0 rotation of the grindin wheel being at an .acute angle with the axis of rotation of the glass, and the grinding edge of the Wheel passing approximately through'the axis of rotation of the glass as it sweeps over the surface thereof, the annular edge of the grinding wheel 'bein shaped to form an abrupt step between t e ground surface and the original surface of the glass on one side through the surface to be ground, and a rotary grinding wheel whose axis crosses the axis of the work and lies in a plane parallel to but spaced from the axis of the work,

said wheel being formed and arran ed to coritact with the ground spherical sur ace of the work along a line extending from one sideof the said surface through the work axis, the grinding surface of the wheel moving along said line by the rotation of the wheel. r

4:. Grinding apparatus, comprising means for rotating the work'about an axis passing through the surface to be ground, a grinding wheel rotary about an axis crossing the axis of the work, said wheel being formed and arranged to contact with the. ground surface of the work along a line extending from one side of the'said surface through the workaxis, the grinding surface of the wheel moving along said line by the rotation of the wheel, and means for moving the work and grinding wheel relatively so as to set their axes in or out of a common-plane.

In testimony whereof I have hereunto set my hand in the presence of two subscribing witnesses. j

WILLIAM TAYLOR. Witnesses: Y MAISIE Memos,

LILLIAN R.Fox. 

